HUMIDIFICATION OF GREEN CANOLA SEED LEADS TO PIGMENT DEGRADATION IN THE ABSENCE OF GERMINATION

Mature canola seeds (Brassica napus cv. Westar) exposed to frost during development frequently contain green pigments that discolor extracted canola oil. The green pigments must be removed from the oil by bleaching, which significantly reduces the oil yield. The quantity of pigment remaining in the oil prior to bleaching is a function of the amount of pigment and the proportion of phytylated pigments in the seeds. The objective of this study was to determine whether the quantity and chemistry of the pigments could be altered by seed humidification after harvest without leading to germination. Intact plants with seed moisture in the range of 700 to 500 g kg(-1) were exposed to -5 degrees C for 3 h. The seeds were harvested at maturity, and analysed for moisture content, pigment content, storage protein, and triacylglycerol before and after exposure to 97% relative humidity for 10 d that increased seed moisture content to 230 g kg(-1). This treatment led to a 25% reduction in total pigment content and a 35% increase in the percentage of dephytylated pigments. In vitro measurements indicated this was the result of chlorophyllase activity. Neither storage proteins nor triacylglycerols were mobilized during humidification. In comparison, unrestricted water imbibition led to changes associated with seed storage protein reserve mobilization within 24 h of initial imbibition. Apparently, humidification treatment has the potential to decrease canola oil pigment content without decreasing seed oil or meal quality and quantity. The recommended humidification procedure attains a seed moisture content of 200 g kg(-1), which can be achieved by a 7-d exposure to 97% RH.